This invention relates to a method of controlling the working pressure of a hydraulic medium delivered by a pump via a remote conrol multiway valve to a thrust piston unit serving at least indirectly to press grinding members of an axially reciprocable and simultaneously rotatable honing tool against the surface of a workpiece recess to be honed during a selectable period.
The invention also relates to an apparatus for carrying out the method including a pump and a remote-controlled multiway valve disposed between the pump and at least one thrust piston unit actuating the axially reciprocable and simultaneously rotatable honing tool.
It is known to radial displace the grinding members of a reciprocal and rotatable honing tool releasably attached to the free end of a hollow honing rod by using a hydraulic thrust piston unit to operate actuating means passing through the honing rod in the longitudinal direction. After the introduction of the honing tool into the recess in the workpiece the thrust piston unit in the known arrangement is always subjected to the full working pressure whose level is mainly determined by the nature of the material to be machined and the thickness of the layer to be removed.
Application of the full pressure to the thrust piston unit when the surface of the recess in the workpiece is still rough and irregular frequently results in jamming of the honing tool in the recess, without the drives for the axial and rotary movements of the honing tool being immediately stopped. As a result the grinding members of the honing tool in particular are subjected to heavy mechanical stress which cause premature wear which may even destroy them. Moreover, worn grinding members give uneven machining of and may damage the workpiece surface. To ensure at least a fairly satisfactory quality of the workpiece surface with the known arrangement, therefore, the grinding members must be changed frequently. However, apart from the considerable expenditure of material, this results in a fairly prolonged duration of machining of each individual workpiece and has very adverse effects on the economics of the honing method.